1. Field of the Invention
The field of the invention relates to injection devices for automatically dispensing premeasured quantities of material, and drive assemblies therefor.
2. Brief Description of the Prior Art
Injection devices such as syringes are widely used in the medical and veterinary fields. They are ordinarily employed by trained personnel who are capable of selecting the appropriate medication and administering the required dosage.
Specialized injection devices have been designed for situations where trained personnel are not available to administer medication. Such devices are usable by persons such as diabetics who self-inject insulin, allergy sufferers who may require an emergency injection of antihistamines or other medication, and other patients where self-injection is either more convenient or necessary.
U.S. Pat. No. 2,752,918 discloses one type of automatically operated injection device. Upon firing an actuating mechanism of this device, a needle is caused to penetrate the skin, medicament is injected through the bore of the needle, and the needle is retracted. The device includes a first coil spring for causing the needle to be projected beyond a nose piece and a second coil spring which is compressed during this procedure. The second spring, upon release of a clutch mechanism, then automatically urges an ampoule and stem rearwardly, causing retraction of the needle.
U.S. Pat. No. 5,137,516 discloses another type of automatically operated injection device. The user first presses the device against the skin in order to move an internal shaft and sleeve assembly. An actuating button is then depressed, causing a button arm to spread the arms of a retention clip. The separation of these arms releases the head of the pusher rod, which is then moved forwardly under the force of a main coil spring. The pusher rod first moves the entire syringe against the force of a syringe spring. Once the needle has penetrated the skin, the syringe plunger is depressed by the pusher rod, causing the syringe to empty. The main spring of the patented device may be recocked upon reloading of a new syringe assembly. Such reloading is accomplished by a force applied by the syringe piston directly upon the pusher rod of the device.
A number of other approaches have been taken for providing automatic injection of various materials. U.S. Pat. Nos. 3,797,489, 4,484,910, 4,902,279 and 5,114,404 provide further examples of this type of device.